It is known in the art to utilize positive displacement superchargers having lobed rotors for supercharging internal combustion engines and for providing compressed air for other purposes. Such a positive displacement supercharger used as an automotive supercharger may include a housing having a rotor cavity in which a pair of parallel rotors having interleaved lobes rotate to compress air drawn into one end of the housing and discharged through an opening in the cavity wall near an opposite end of the housing. The rotors may be belt driven by the engine through a pulley, or through a gear train, connected directly to the pair of rotors.
Superchargers are very sensitive to running clearances. Tighter clearances between the two rotors and between the rotors and the rotor cavity wall improve flow and efficiency by reducing leakage of hot boost air to the intake side. Problems with scuffing limit the tightest practical operating clearances that are possible. Scuffing is more likely to occur during continuous high load operation from thermal growth resulting from high outlet air temperatures. Rotor fits generally compromise efficiency to maintain clearance and prevent scuffing.
In high performance and racing engines, flexible tip seals are sometimes applied along the outer edges of the rotors to seal the clearances and provide improved performance and efficiency. However, short wear life generally makes these applications unsuitable for use in general production vehicles.